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            "title": "Reorder Routes to Make All Paths Lead to the City Zero",
            "titleSlug": "reorder-routes-to-make-all-paths-lead-to-the-city-zero",
            "content": "<p>There are <code>n</code> cities numbered from <code>0</code> to <code>n - 1</code> and <code>n - 1</code> roads such that there is only one way to travel between two different cities (this network form a tree). Last year, The ministry of transport decided to orient the roads in one direction because they are too narrow.</p>\n\n<p>Roads are represented by <code>connections</code> where <code>connections[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> represents a road from city <code>a<sub>i</sub></code> to city <code>b<sub>i</sub></code>.</p>\n\n<p>This year, there will be a big event in the capital (city <code>0</code>), and many people want to travel to this city.</p>\n\n<p>Your task consists of reorienting some roads such that each city can visit the city <code>0</code>. Return the <strong>minimum</strong> number of edges changed.</p>\n\n<p>It&#39;s <strong>guaranteed</strong> that each city can reach city <code>0</code> after reorder.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/05/13/sample_1_1819.png\" style=\"width: 311px; height: 189px;\" />\n<pre>\n<strong>Input:</strong> n = 6, connections = [[0,1],[1,3],[2,3],[4,0],[4,5]]\n<strong>Output:</strong> 3\n<strong>Explanation: </strong>Change the direction of edges show in red such that each node can reach the node 0 (capital).\n</pre>\n\n<p><strong>Example 2:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2020/05/13/sample_2_1819.png\" style=\"width: 509px; height: 79px;\" />\n<pre>\n<strong>Input:</strong> n = 5, connections = [[1,0],[1,2],[3,2],[3,4]]\n<strong>Output:</strong> 2\n<strong>Explanation: </strong>Change the direction of edges show in red such that each node can reach the node 0 (capital).\n</pre>\n\n<p><strong>Example 3:</strong></p>\n\n<pre>\n<strong>Input:</strong> n = 3, connections = [[1,0],[2,0]]\n<strong>Output:</strong> 0\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>2 &lt;= n &lt;= 5 * 10<sup>4</sup></code></li>\n\t<li><code>connections.length == n - 1</code></li>\n\t<li><code>connections[i].length == 2</code></li>\n\t<li><code>0 &lt;= a<sub>i</sub>, b<sub>i</sub> &lt;= n - 1</code></li>\n\t<li><code>a<sub>i</sub> != b<sub>i</sub></code></li>\n</ul>\n",
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                    "code": "class Solution {\npublic:\n    int minReorder(int n, vector<vector<int>>& connections) {\n        \n    }\n};",
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                    "code": "class Solution(object):\n    def minReorder(self, n, connections):\n        \"\"\"\n        :type n: int\n        :type connections: List[List[int]]\n        :rtype: int\n        \"\"\"\n        ",
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                    "code": "/**\n * @param {number} n\n * @param {number[][]} connections\n * @return {number}\n */\nvar minReorder = function(n, connections) {\n    \n};",
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                    "code": "# @param {Integer} n\n# @param {Integer[][]} connections\n# @return {Integer}\ndef min_reorder(n, connections)\n    \nend",
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                    "code": "class Solution {\n    func minReorder(_ n: Int, _ connections: [[Int]]) -> Int {\n        \n    }\n}",
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                    "code": "object Solution {\n    def minReorder(n: Int, connections: Array[Array[Int]]): Int = {\n        \n    }\n}",
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                    "code": "impl Solution {\n    pub fn min_reorder(n: i32, connections: Vec<Vec<i32>>) -> i32 {\n        \n    }\n}",
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                    "code": "-spec min_reorder(N :: integer(), Connections :: [[integer()]]) -> integer().\nmin_reorder(N, Connections) ->\n  .",
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            "hints": [
                "Treat the graph as undirected. Start a dfs from the root, if you come across an edge in the forward direction, you need to reverse the edge."
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